1. Field of the Invention
The present invention generally relates to a signal transmission and reception device which performs communications by using impulse UWB (Ultra Wide Band) signals.
2. Description of the Related Art
In spread spectrum communications, in order to obtain a large variety of correlation characteristics, it is proposed to convert Pseudorandom Noise (PN) codes used in DSSS (Direct Sequence Spread Spectrum) to Return-to-Zero (RZ) codes, and multiply the RZ codes by data. For example, Japanese Laid-Open Patent Application No. 4-347943 (referred to as “reference 1” hereinafter) discloses a technique in this field. Since each PN code can have a positive or a negative value, by converting the PN codes to the RZ codes, output data becomes zero in a certain time period of the PN code, thus, each RZ code can have three types of values, that is, a positive, zero, or a negative value.
On the other hand, a UWB-IR (UWB-Impulse Radio) communication system is attracting attention since the UWB-IR system is capable of large capacity data transmission and is able to accommodate a large number of users. Since impulses shorter than 1 ns are used in the UWB-IR system, and the corresponding frequency band is at a few GHz, conventional radio communications are not interfered with; thus the frequency band can be shared.
For example, it is proposed that a signal transmission device supporting the UWB-IR communications performs spread modulation and RZ conversion of the PN codes on data carried by the carrier, and converts the resulting data to impulse radio signals. Further, a signal reception device for receiving the impulse radio signals has been developed. For example, Japanese Laid-Open Patent Application No. 2006-114980 (referred to as “reference 2” hereinafter) discloses a technique in this field.
In addition to the capability of large capacity data transmission, when the UWB-IR communication system is used in data transmission, it is possible for the transmitter to measure positions with high precision. Further, when a receiver supporting the UWB-IR communications is used together with the transmitter, it is possible to measure distances with high precision.